The present invention relates to apparatus for attenuating light passing from one optical fiber to another by varying the distance from one optical fiber end face to the end face of the opposed optical fiber and particularly relates to an optical fiber attenuator of this type which is compact in construction and readily and easily utilized. The present invention also relates to a connecting element for securing an optical fiber connecting ferrule in an optical fiber assembly.
In many fiber optics systems, optical fiber attenuators are used to reduce energy levels in the transmission of light from a transmitting station to a receiving station. Also, for evaluating fiber optics systems, optical fiber attenuators are used to simulate transmission losses over long distances. A fiber optic attenuator is a device for adjustably spacing the end faces of a pair of optical fibers. By spacing these end faces a greater extent relative to one another, the attenuation of the light transmitted from one optical fiber to the other is increased. Conversely, the degree of attenuation of light transmitted between two opposed end faces is decreased as the spacing therebetween is decreased.
One criteria for an effective fiber optic attenuator is that it must be compatible with standard (e.g., "SMA" type) fiber optic connectors. Standard connectors typically comprise ferrules, including an elongated shaft through which the optical fiber passes, the optical fiber terminating adjacent the end face of the shaft. A pair of axially spaced flanges are disposed adjacent the opposite end of the ferrule for use with conventional elements for connecting the ferrules one to the other. Thus, any commercially successful fiber optic attenuator must be constructed in a manner to enable connection with these standard connectors.
There are also many fiber optic applications which require the use of a very small and compact fiber optic attenuator. In one such prior optical fiber attenuator, the standard fiber optic connector is disposed in a connector interface adaptor by threading a nut over the connector onto the adaptor. The adaptor is then threaded into a large-diameter, externally-threaded sleeve bearing an external locking nut. That sub-assembly is threadedly received within an outer housing, the opposite end of which receives a connector. By threading the inner and outer housings relative to one another, the spacing between the end faces of the optical fibers secured respectively to the inner and outer housings may be adjusted whereby the attenuation is likewise adjusted. A fiber optic attenuator of this type is manufactured and sold by Fotec, Inc., Boston, Mass., under the tradename "The Fotec A430 Fiber Optic Attenuator." While this attenuator serves its purpose, it is bulky, for example, has a length at least five or six times the length of each of the ferrules of the standard connector and a diameter well in excess of five times the diameter of the shaft of the ferrule.
It has also been recognized by those skilled in this art that the shafts of the standard ferrules must be fully inserted into a bore to provide coaxial orientation. Thus, known attenuators maintain the entire length of the shaft of the standard ferrule in the bore of a corresponding part and displace the parts axially relative to one another in order to maintain that coaxial relation. However, it has been discovered that the degree to which the shaft can be inserted into the bore can be varied to adjust the attenuation without substantially affecting the linearity of the attenuation introduced by the coupler. That is, the shaft of the standard ferrule may be withdrawn from a corresponding bore of an attenuator to a limited extent and to the desired degree of attenuation so that limited misalignment in the coaxial relation of the ferrule shafts can be tolerated.
In the prior art, the degree of concentricity or coaxial alignment which needs to be maintained between the opposed ferrules, particularly at small gaps, is degraded because such concentricity is transferred through several sets of threads. That is, there is side play during the threading action which axially misaligns the ferrules which, at small gaps, may inhibit or even eliminate transmission of light from one optical fiber to the other. In the present invention, both ferrules are maintained in a common bore which maintains the coaxial alignment of the ferrules, particularly at smaller gaps.
Additionally, in many optical fiber applications it is customary to connect long lengths of optical fiber to connectors using lock nuts. Typically, the end of the optical fiber is passed through a bore in a standard connector ferrule to project from its opposite end. The fiber is adhesively secured in the bore and the projecting end removed and polished. If this is done without first threading the lock nut onto the optical fiber, i.e., prior to passing the optical fiber into the bore of the ferrule, great difficulty obtains in applying the lock nut to the ferrule and associated connecting part and about the optical fiber. To alleviate that problem, applicants use optical fiber connectors, e.g., lock nuts, which have an axially extending slit along one side thereof for passing the optical fiber through the slit into the bore of the connector. Consequently, even after connecting the optical fiber to the ferrule, for example, the connector or lock nut can be disposed about the optical fiber by passing the fiber through the slit into the bore of the connector.
Accordingly, in accordance with the present invention, there is provided a fiber optic attenuator which eliminates or minimizes the foregoing and other problems associated with prior fiber optic attenuators and provides a compact, relatively inexpensive and readily and easily used fiber optic attenuator having various advantages in construction, mode of operation and result. Particularly, the present invention provides an attenuator assembly comprised of a sleeve having a throughbore for receiving at opposite ends the standard ferrules of optical fiber connectors. Each ferrule, of course, carries the optical fiber and, when the ferrule shafts are disposed in the bores, the end faces of the optical fibers lie in spaced opposition one to the other. The sleeve is externally threaded and receives an internally threaded adjuster about one end. The adjuster has a radially inwardly directed flange for disposition between the end face of the sleeve and a flange on the connector. The adjuster itself is externally threaded to receive a ferrule lock nut thereabout. The ferrule lock nut has a radially inwardly directed flange for engaging the standard connector whereby the connector is clamped between the ferrule lock nut and the adjuster. The other ferrule is retained in fixed position in the opposite end of the sleeve by a ferrule lock nut. An additional lock nut is threaded about the sleeve to lock the adjuster in adjustable axial position along the sleeve.
With the foregoing construction, the sleeve carrying the fixed ferrule may be screwed in or out relative to the adjuster and the ferrule lock nut carried by the adjuster whereby the spacing between the end faces of the ferrules and hence between the opposed end faces of the optical fibers can be varied. Jamming the lock nut against the adjuster then locks the ferrule carried by the adjuster and ferrule lock nut in its adjusted position. Hence, by this threading action, a predetermined attenuation is afforded.
It will be appreciated that the shaft of the standard connector ferrule carried by the adjuster and ferrule lock nut is moved in and out of the bore of the sleeve. While general axial alignment is maintained between the fiber faces, it has been found that as the desired degree of attenuation increases as the gap between the end faces of the optical fibers increases, the coaxial orientation of the two fiber end faces becomes less critical so that it is tolerable to introduce a degree of misalignment without substantially affecting the linearity of the attenuation introduced by the coupler.
With the foregoing described construction, the attenuator may be constructed in a relatively compact manner. For example, the length of the attenuator hereof may be no greater than the combined length of two standard ferrules at minimum attenuation and that, plus the length of a portion of one ferrule shaft at maximum attenuation. Additionally, the diameter of the attenuator hereof has a cross-section no greater than about five times the diameter of the shaft of the ferrule. In this manner, a relatively compact attenuator is provided.
In accordance with a further aspect of the present invention, the lock nuts are provided along one side with an axially extending slit. The slit is sized to permit passage of the optical fiber through the slit into the bore of the lock nut. In this manner, the lock nut may be applied to the optical fiber and, hence, the part to which it is connected, after the fiber has been secured to the ferrule.
In a preferred embodiment according to the present invention, there is provided apparatus for adjusting the attenuation of light passing between a pair of optical fibers disposed in spaced end-to-end relation one to the other, comprising a pair of elongated, generally cylindrical, ferrules mounting respective optical fibers generally axially therealong with the fibers terminating in end faces substantially adjacent the respective ends of the ferrules, a sleeve having a throughbore for receiving the ferrules through its opposite ends with the ferrule ends in opposition to one another and the fiber end faces in spaced opposing relation to one another, at least a portion of the sleeve being externally threaded and an internally threaded adjuster for threaded engagement about one end of the sleeve, the adjuster having an opening at one end for receiving one of the ferrules and an externally threaded portion, means for retaining the other of the ferrules in the other end of the sleeve and an internally threaded nut for threaded engagement with the externally threaded portion of the adjuster and having an opening at one end for receiving the one ferrule. Means are cooperable between the one ferrule and at least one of the adjuster and the nut for retaining the one ferrule in the sleeve and responsive to threading action between the adjuster and the sleeve for axially displacing the one ferrule relative to the other ferrule whereby the ends of the ferrules and the end faces of the optical fibers carried thereby are adjustably spaced one from the other.
In a further preferred embodiment according to the present invention, there is provided apparatus for adjusting the attenuation of light passing between a pair of optical fibers carried by a pair of elongated, generally cylindrical, ferrules disposed in spaced end-to-end relation one to the other, comprising a sleeve having a throughbore for receiving the ferrules through its opposite ends with the ferrule ends in opposition to one another and the fiber end faces in spaced opposing relation to one another, at least a portion of the sleeve being externally threaded, an internally threaded adjuster for threaded engagement about one end of the sleeve, the adjuster having an opening at one end for receiving one of the ferrules and an externally threaded portion, means for retaining the other of the ferrules in the other end of the sleeve and an internally threaded nut for threaded engagement with the externally threaded portion of the adjuster and having an opening at one end for receiving the one ferrule, the internally threaded nut having a radially inwardly directed flange defining the opening therein for receiving the one ferrule. Means are provided carried by at least one of the adjuster and the nut and cooperable with the one ferrule for retaining the one ferrule in the sleeve and responsive to threading action between the adjuster and the sleeve for axially displacing the one ferrule relative to the other ferrule whereby the ends of the ferrules and the end faces of the optical fibers carried thereby are adjustably spaced one from the other.
In a further preferred embodiment according to the present invention, there is provided an optical fiber coupler/attenuator of the type for optically coupling first and second elongated optical fiber connector portions together, the coupler/attenuator including a unitary, substantially hollow tubular member having first and second ends adapted for axially receiving the first and second optical fiber connector portions, respectively, therein, the hollow tubular member maintaining the first and second optical fiber connectors substantially coaxial with one another and means coupled to the hollow tubular member first end for permitting manual adjustment, over a range, of the degree of insertion of the first fiber connector portion into the hollow tubular member and for locking the position of the first fiber connector portion with respect to the tubular member so as to maintain the adjusted degree of insertion.
In a further preferred embodiment according to the present invention, there is provided a method of adjusting the optical attenuation between two elongated optical fiber connector cylindrical ferrule portions optically coupled together via a substantially hollow tubular member, the hollow tubular member insertably receiving the ferrule portions therein and maintaining the two optical fiber connector ferrule portions substantially coaxial with one another, the method comprising adjusting the positional relationship of at least one of the ferrule portions with respect to the hollow tubular member so as to define a relative position whereat the one ferrule portion is less than fully inserted into the hollow tubular member and, subsequent to said adjusting step, locking the one ferrule portion in the less than fully inserted relative position.
In a further preferred embodiment according to the present invention, there is provided apparatus for securing an optical fiber connector in a connecting assembly comprising a sleeve for receiving the optical fiber connector and having a threaded portion, a connecting element for locking the optical fiber connector in the sleeve and defined by side walls having a threaded portion for threadedly engaging the threaded portion of the sleeve and an axial bore for receiving the optical fiber and the connecting element having a slot through the side walls extending axially and sized to enable the optical fiber to pass through the slot into the bore of the connecting element.
Accordingly, it is a primary object of the present invention to provide a novel and improved fiber optic attenuator which is compact in construction, inexpensive to fabricate, and provides a very fine attenuation adjustment as well as a method for adjusting the optical attenuation of coupled optical fibers. A further object hereof is to provide a connecting element for locking the optical fiber ferrule to another connecting part in a manner enabling application of the connecting element after the optical fiber is secured to the ferrule.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.